Heart-rate profile during exercise a strong predictor of sudden death

Heart-rate profile during exercise and recovery is a strong predictor of sudden death, a French study has found. "These findings may have clinical implications in terms of the early identification of high-risk subjects and raise the possibility of primary prevention," write the authors in the 12th May edition of the New England Journal of Medicine.In order to explore the possibility that abnormalities in the control of heart rate in apparently healthy men may indeed precede clinical symptoms and may allow early identification of persons at increased risk for death, Dr. Jouven, at Hopital Europeen Georges Pompidou in Paris, and colleagues performed standardized graded exercise testing between 1967 and 1972 on 5713 healthy men ages 42 to 53 years. The researchers excluded persons with known or suspected cardiovascular disease, systolic blood pressure greater than 180 mm Hg, or abnormalities on a resting 12-lead electrocardiogram.During a mean follow-up of 23 years, there were 1516 deaths from all causes, including 81 sudden cardiac deaths and 129 nonsudden deaths from MI.After adjustments were made for age, use or nonuse of tobacco, level of physical activity, presence or absence of diabetes, body-mass index, basal systolic blood pressure, cholesterol level, presence or absence of a parental history of sudden death or myocardial infarction, and exercise duration, the risk of sudden death increased progressively with the resting heart rate.The risk of sudden death was 3.5 times higher among those in the highest quintile of resting heart rate compared with the lowest quintile (pConversely, those in the lowest quintile for heart rate increase during exercise had 4.0 times the risk of sudden death, 1.2 times the risk of nonsudden death, and 1.5 times the overall risk of death compared with those in the highest quintile.Subjects with a heart-rate recovery of less than 25 beats per minute (the lowest quintile) had 2.1 times the risk of sudden death and 1.3 times the risk of death from any cause. Only the risk of nonsudden cardiac death was not associated with heart rate recovery."The mechanism underlying the present findings is not immediately obvious," the researchers note. They suggest that it could involve an impaired ability to increase not only vagal but also sympathetic activity to appropriate levels, which in turn, may be explained by a reduced baroreflex sensitivity that favours circulatory collapse during ventricular tachycardia, a condition that precipitates ventricular fibrillation and sudden death. "The clinical counterpart of this defective physiological response would be a reduced ability to increase heart rate during exercise to the maximum extent - which represents the most puzzling of the features that we found to be associated with an increased risk of sudden death," they add. They suggest that for apparently healthy persons with a heart-rate profile that is associated with a high risk of sudden death, a possible therapeutic approach might be the correction of the autonomic imbalance. In addition to traditional management of cardiovascular risk factors, initiation of a regular exercise-training program should be recommended, they write.Reference...